Hydrocarbon separation process and apparatus

Description

Introduction and Background

[0001] This invention relates to a process, and the apparatus for effecting such a process, for the cryogenic fractionation of gaseous hydrocarbon feeds to extract and recover the valuable heavier components thereof. The invention is particularly concerned with a process for high recovery of ethane and heavier components from a natural gas feed. The process is not limited to the recovery of paraffinic compounds such as ethane found in natural gas, but also, for example, to olefins such as ethylene often found in gases associated with petroleum refining or petrochemicals manufacture.

[0002] Conventional processes to effect very high recovery of ethane and heavier components from natural gas typically utilise a combination of heat exchange, turbo-expansion, phase separation and fractionation steps. The use of turbo-expansion produces work, which can be used to drive a compressor to supplement residual gas compression, and by removing energy from the feed gas produces low temperature.

Description of Prior Art

[0003] In such conventional processes feed gas is partially condensed in a heat exchange system, which typically includes rewarming residual vapour and may include other cold streams such as refrigerant from a mechanical refrigeration cycle. Partial condensation results in a liquid stream, enriched in the valuable heavy components being recovered and a vapour stream, which may undergo further partial condensation steps. These partial condensation steps result finally in one or more liquid streams and a high pressure vapour stream. The liquid streams are expanded and fed to a demethaniser column, which removes the majority of the methane and lighter components, to produce a stable liquid stream. The high pressure vapour stream is work expanded giving a two phase stream which is fed to the demethaniser at a point above the expanded liquid streams.

[0004] It is conventional for the demethaniser column to be refluxed with a stream colder than the expander exhaust. A number of processes have been proposed, which differ in their selected demethaniser reflux stream. These processes do however share the principle of judiciously using heat exchanger surface area to make good use of the available refrigeration and to thus give lower process temperatures. Losses of the valuable ethane and heavier components in the demethaniser overheads can thus be reduced without decreasing the demethaniser column pressure and therefore without excessive power requirement.

[0005] These processes give an improvement over traditional processes, which use the expander exhaust as the top feed to the demethaniser. Increasing recovery of ethane and heavier components in these traditional processes requires a reduction in demethaniser and expander exhaust pressure to reduce temperatures. Very high ethane recovery can therefore result in uneconomically high power requirements in either recompression of the residual vapour to required product pressure, external refrigeration to increase liquids condensation or in feed gas compression which also increases liquids condensation.

[0006] It is common for the selected source of demethaniser reflux to be lean in the components being recovered. A particularly effective reflux stream is that derived from the demethaniser overheads, which in a process effecting very high recovery of ethane from natural gas may be nearly pure methane. A conventional overhead condenser, condensing overhead vapour at column pressure, can not usually be utilised due to the absence of process streams at a lower temperature to provide the necessary refrigeration. In the process of US patent 4,889,545, a portion of the demethaniser overhead vapour is compressed in a standalone compressor, such that it can be condensed in heat exchange with other process streams to reflux the demethaniser.

[0007] US Patents 4,171,964 and 4,157,904 describe processes in which streams relatively rich in ethane are sent to the top of the demethaniser to act as reflux, and thus do not provide very high recovery of ethane. GB 2,309,072 and WO 98/50742 disclose hydrocarbon gas processing apparatus wherein a recycle stream is used to reflux the demethaniser.

[0008] A configuration in which a portion of the residue gas, which has been rewarmed and compressed to a pressure suitable for export, is recycled, condensed, subcooled and expanded to reflux the demethaniser column shown in Figure 1. This configuration is less thermodynamically efficient than that of a standalone compressor, due to the losses inherent in warming and re-cooling the residue vapour. The process is however simpler as a standalone compressor is not required.

[0009] The pressure at which the recycle stream is cooled and condensed will typically be optimised to minimise residual gas compression power requirement. It is desirable to subcool the recycle stream to within a small approach to the demethaniser overhead temperature, which is the coldest stream in the process. This minimises evolution of vapour on expanding the liquid to column pressure and therefore maximises the liquid available to reflux the rising vapour in the column. At lower recycle stream pressures, compression power requirements are reduced, but the cooling curve becomes less linear and a pinch can occur which limits the temperature to which the recycle stream can be cooled.

Summary of Invention

[0010] According to one aspect of the invention there is provided a process for the separation of a heavier hydrocarbon fraction from a gaseous feed comprising a mixture of hydrocarbons, which process comprises:

(a) cooling the gaseous feed to produce a partially condensed stream

(b) separating the partially condensed stream to form a first liquid stream and a first gaseous stream

(c) subcooling at least a portion of the first liquid stream

(d) expanding said subcooled stream

(e) passing at least a portion of the expanded stream from (d) as a liquid feed to a fractionation column

(f) producing a cooled stream by cooling a separated lights fraction of the feed

(g) recovering said heavier hydrocarbon fraction as a bottoms fraction from said column

characterised in that (i) at least a part of the subcooling required in subcooling step (c) is provided by transfer of heat to the expanded stream from (d), (ii) at least a portion of the cold required to cool the separated lights fraction to produce said cooled stream (f) is provided by transfer of heat to the expanded stream from (d), and (iii) at least a portion of said cooled stream (f) is introduced to an upper part of the column.

[0011] It will be appreciated that as a result of having been expanded in step (d) and subjected to a heat transfer operation to provide at least part of the subcooling required from step (c), the feed to the fractionation column will be in an at least partially evaporated state.

[0012] In a preferred manner of operation according to the invention at least a part of the subcooling required in subcooling step (c) is provided by transfer of heat to overhead vapour from said fractionation column. When operated in this manner overhead vapour from the fractionation column may be heated in heat exchange with the first liquid stream from step (b) prior to expansion. More preferably a process is provided wherein overhead vapour from the fractionation column and the expanded stream from step (d) are heated in heat exchange with said first liquid stream from step (b) prior to expansion in a single heat exchanger.

[0013] It will be appreciated that in accordance with the invention, net refrigeration available within the heat exchanger may be used to cool said stream (f). Preferably the cooled stream (f) comprises a recycle stream derived from overheads from the fractionation column, and is used to reflux the top section of the fractionation column.

[0014] By heat-exchanging the first liquid stream and the separated lights fraction with the expanded stream from (d), against the evaporating stream derived from the subcooled stream, a stream of lower temperature is produced that ultimately leads to reduced overheads temperature and increased recovery.

Description of Drawings

[0015] Embodiments of the invention will now be described in more detail with particular reference to the accompanying drawings of which:

[0016] Figure 1 describes a prior art process for the separation of heavier hydrocarbons from a gaseous hydrocarbon feed.

[0017] Figure 2 describes a first embodiment of the present invention wherein a heavier hydrocarbon fraction may be separated from a gaseous hydrocarbon feed. The feed is partially condensed and then separated into the first gaseous stream and the first liquid stream. The first liquid stream is then subcooled in the heat exchanger, expanded, at least partially evaporated, and then passed to the fractionation column.

[0018] Figure 3 displays a variation of the first embodiment wherein the first liquid stream is separated into a further liquid stream and a further gaseous stream, and the further liquid stream is then transferred to the fractionation column via the heat exchanger, as in Figure 2.

[0019] Figure 4 displays another variation of the first embodiment wherein the first gaseous stream is separated into a further gaseous stream and a further liquid stream, and then both streams are transferred to the fractionation column.

[0020] Figure 5 describes a second embodiment of the invention for separating a heavier hydrocarbon from a gaseous hydrocarbon feed wherein the first liquid stream and the first gaseous stream are transferred to a reequilibration device which produces a first output and a second output. The first output, which is richer in heavier hydrocarbons, is then transferred to the fractionation column via the heat exchanger as in Figure 2.

[0021] In a first embodiment of the invention a process is provided wherein overhead vapour from the fractionation column is rewarmed, compressed and cooled to provide a recycle stream and a residue gas product. Preferably the overhead vapourfrom the fractionation column and the expanded stream from step (d) are heated in heat exchange with the subcooled first liquid stream from step (b) prior to expansion in a single heat exchanger. This enables small temperature differences to be achieved between cooling and warming streams and gives improved use of available refrigeration.

[0022] The process of the present invention according to this embodiment, as shown in Figure 2, offers an improvement over the conventional residue gas recycle process, by enabling subcooling of the recycle stream to a close approach to the demethaniser overheads temperature at lower recycle pressures than is conventionally possible. Alternatively for a fixed recycle pressure, the recycle stream can be subcooled to a lower temperature. This can result in reduced process power requirement, increased recovery of the desired heavy hydrocarbons or a realisation of both of these effects.

[0023] A particular advantage of the process of the invention according to this embodiment is that liquid from the first separator may be subcooled and expanded, providing refrigeration at a temperature level such that it can contribute to the condensation/subcooling of the recycle stream and subcooling of liquid from the first separator. This makes improved use of available refrigeration to remove the restrictive temperature 'pinch' such that the recycle stream can be subcooled to a smaller temperature approach to the demethaniser residue gas. This enables high recovery of the desirable components to be achieved with lower recycle pressures and lower compression power requirements.

[0024] Thus in a preferred aspect, this embodiment may also include process elements whereby net refrigeration available within the heat exchanger is used to cool a further process stream comprising a separated lights fraction of the feed. Preferably this further process stream comprises a recycle stream derived from overheads from the fractionation column. More preferably at least a portion of this recycle stream is condensed/subcooled and returned to an upper part of the fractionation column.

[0025] The liquid from the first separator having been subcooled, expanded and evaporated may be fed to the demethaniser column at a mid-stage, as a two phase stream. The location of the feed point may be optimised to maximise process efficiency. In addition to the subcooling, expanding and evaporation of liquid from the first separator, the conventional residual gas recycle process can be further improved by the addition of other process features. These features give improved demethaniser rectification, and for a given recovery of ethane, the required recycle flow of residue gas to reflux the demethaniser is reduced and therefore overall power requirement is reduced.

[0026] In one variation of this first embodiment a process is provided wherein the first liquid stream is expanded and separated to give a further gaseous stream and at least a portion of the remainder is subjected the processes of steps (c) and (d).

[0027] This feature of expanding the liquid from the first separator to an intermediate pressure to flash off the lighter components is shown in Figure 3. The methane rich flash vapour may be separated from the liquid, which may subsequently be subcooled, expanded and evaporated. The flash vapour may be combined with the residual gas recycle stream. For a given reflux flow, the recycle flow is reduced thereby reducing compression power.

[0028] Thus the invention also provides a process wherein at least a part of the further gaseous stream is transferred to the fractionation column. Preferably this further gaseous stream or a portion thereof is introduced into the fractionation column at a point above the liquid feed. More preferably the further gaseous stream or a portion thereof is cooled, and optionally expanded prior to its introduction into the fractionation column.

[0029] As described above, it is further within the scope of the invention to provide a process wherein the further gaseous stream or a portion thereof is combined with the recycle stream prior to being transferred to the fractionation column. Preferably the further gaseous stream or a portion thereof and the recycle stream are cooled and expanded to produce an at least partially condensed (e.g. liquid) stream which is introduced into the fractionation column. Most preferably the first gaseous stream or a portion thereof and the recycle stream are introduced into the fractionation column at a point above the liquid feed.

[0030] In another variation of this first embodiment a process is provided wherein the first gaseous stream is work expanded and separated to give a further gaseous stream and a further liquid stream, said further gaseous stream is partially condensed in a heat exchanger and then fed to the fractionation column. It is preferred that in the process the further gaseous stream is introduced into the fractionation column at a point above the liquid feed. Preferably the further liquid stream is also introduced into the fractionation column.

[0031] It is also within the scope of this variation to provide a process wherein the further gaseous stream is partially condensed in heat exchange with the expanded stream from step (d). Preferably overhead vapour from the fractionation column and the expanded stream from step (d) are heated in heat exchange with the first liquid stream from step (b) prior to expansion.

[0032] The process of the invention may also be operated in a manner wherein one of said first gaseous stream and said first liquid stream is expanded and separated to give a further gaseous stream and a further liquid stream, or wherein both of said first gaseous stream and said first liquid stream are expanded, combined and separated to give a further gaseous stream and a further liquid stream.

[0033] In a preferred aspect a process is provided wherein the first gaseous stream may be work expanded prior to separation.

[0034] The particular feature described above of separating the two phases of the expander exhaust stream, and subsequently partially condensing the vapour phase in heat exchange with other process streams is shown in Figure 4. The partially condensed vapour phase may be fed to the column at a separate point above that at which the liquid phase is fed.

[0035] Contacting the vapour phase of a partially condensed feed gas with a light hydrocarbon stream can selectively remove the heavier components from that vapour. A process utilising a wash column operating at high pressure to separate the heavier components from a gaseous hydrocarbon feed is described in our copending UK patent application no. 9826999.6 (WO 00/34213). This procedure may be incorporated in the process of the present invention whereby a residual vapour is produced at high pressure from the wash column. Liquid from the wash column is passed to a low pressure fractionation column which produces a stabilised liquid product and a lower pressure residual vapour stream.

[0036] In the application of high propane recovery from natural gas, vapour from the top tray of a deethaniser column can be partially condensed to provide reflux to both the deethaniser and the high-pressure wash column. Whilst sufficient reflux can be generated for high recovery of propane and heavier components from natural gas, in most cases, sufficient reflux cannot be generated economically by this route to effect high recovery of ethane and heavier components. For economical high ethane recovery from natural gas, an alternative reflux stream for the high-pressure wash column must therefore be found.

[0037] In a second embodiment of the invention, the process of subcooling, expanding and evaporating liquid to provide refrigeration at a low temperature level can be applied to a flowsheet using a two column process such that it is suitable for high recovery of ethane and heavier components, as shown in Figure 5.

[0038] In general terms, in the process of this invention according to this embodiment, high pressure vapour from the first separator undergoes work expansion to a medium pressure and is fed to a mid-stage of a wash column. The liquid from the first separator may be expanded to medium pressure and fed to the bottom of the wash column.

[0039] The wash column overheads, at a medium pressure, may be partially condensed in a well integrated heat exchange operation. A portion of the liquid may be used to reflux the wash column and the remaining portion expanded and used to reflux the demethaniser. Liquid from the bottom of the wash column may then be subcooled, expanded and rewarmed prior to being fed to the demethaniser column. By this arrangement refrigeration is provided at a temperature level such that it can contribute to the partial condensation of the wash column overheads.

[0040] Thus in the second embodiment of this invention there is provided a process wherein the first gaseous stream and the first liquid stream are fed to a reequilibration device which produces a first output, richer in heavier hydrocarbons than the first liquid stream, and a second output, leaner in heavier hydrocarbons than the first gaseous stream, wherein the second output is cooled and partially condensed and directly or indirectly fed to an upper part of the fractionation column as said cooled stream (f) and wherein the first output (which comprises at least a portion of the first liquid stream from step (b)) is subjected to the processes of steps (c) and (d). The reequilibration device may preferably be a high pressure wash column.

[0041] In a preferred manner of operation the first gaseous stream is work expanded before being fed to the reequilibration device.

[0042] It is within the scope of this embodiment to provide a process wherein the second output is partially condensed in heat exchange with the expanded stream from step (d). Preferably the second output is partially condensed and at least a portion of the first liquid stream from step (b) is subcooled in heat exchange with both the overhead vapour from the fractionation column and the expanded stream from step (d).

[0043] The invention also provides a process according to this second embodiment wherein the partially condensed second output is fed to a separator, which produces an additional gaseous stream and an additional liquid stream, wherein at least a portion of the additional liquid stream is fed to an upper part of the fractionation column. Preferably at least a portion of said additional liquid stream is also fed to the reequilibration device.

[0044] In a further aspect of this embodiment, the additional gaseous stream may be warmed to produce a residual gas product. Preferably the additional gaseous stream is warmed in heat exchange with at least a portion of the first liquid stream from step (b) prior to expansion. More preferably the additional gaseous stream and the overhead vapour from the fractionation column are warmed in heat exchange with the first liquid stream from step (b) prior to expansion, and the second output from the reequilibration device.

[0045] In both embodiments described above, an overhead fraction from the fractionation column may be warmed, and successively compressed and cooled to produce a residue gas product. In the first embodiment of the invention, a portion of this residue gas product is recycled back to reflux the top section of the fractionation column.

[0046] The invention further provides apparatus for the separation of a heavier hydrocarbon fraction from a gaseous feed comprising a mixture of hydrocarbons, wherein the mixture is cooled, partially condensed, separated into a first liquid stream and a first gaseous stream and at least a portion of each of the first liquid stream and the first gaseous stream are passed to a fractionation column in which said separation is carried out, which apparatus comprises:

(i) conduit means for transferring at least a portion of the first liquid stream to a heat exchanger in which said portion is subcooled,

(ii) means for expanding said subcooled stream,

(iii) conduit means for transferring at least a portion of said expanded stream to the heat exchanger in which the subcooling is effected, whereby at least a part of the subcooling is provided by transfer of heat to the expanded stream.

(iv) conduit means for introducing a cooled stream produced by cooling a separated lights fraction of the feed to an upper part of the column, at least a portion of the cold required to cool the separated lights fraction being provided by transfer of heat to said expanded stream

[0047] The invention further provides apparatus as described above wherein the cooled, partially condensed mixture is separated into a first gaseous stream and a first liquid stream in a first separator, and said apparatus further comprises means for expanding the first liquid stream and means for separating the first expanded liquid stream into a further gaseous stream and a further liquid stream, wherein the further liquid stream is transferred to the heat exchanger.

[0048] The above-defined apparatus may further comprise means (e.g. an expansion turbine) for partially condensing the first gaseous stream, separation means for separating at least a portion of the partially condensed stream into a further gaseous stream and a further liquid stream, and means for transferring at least a portion of the further gaseous stream to the fractionation column.

[0049] The apparatus of the invention may be adapted for carrying out the second process embodiment of the invention, wherein the cooled, partially condensed mixture is separated into a first gaseous stream and a first liquid stream in a first separator. In this case the apparatus additionally includes

(a) means for work expanding said first gaseous stream,

(b) means for expanding said first liquid stream,

(c) a reequilibration device which is arranged to receive said expanded first gaseous stream and said expanded first liquid stream, and produces a first output which is richer in heavier hydrocarbons than said first expanded liquid stream, and a second output which is leaner in heavier hydrocarbons than said first gaseous stream,

(d) conduit means for transferring at least a portion of said second output to the fractionation column, and

(e) conduit means for transferring said first output to the heat exchanger.

Description of Specific Embodiments

Embodiment 1

[0050] The invention is described below in terms of a process for high ethane recovery. The description should be read in conjunction with the flow diagram in Figure 2.

[0051] A feed gas at an elevated pressure 2 is passed through heat exchange system 4 where it is cooled and partially condensed. The liquid phase 18 is separated from the uncondensed vapour phase 10 in vapour/liquid separator 8. A first gaseous stream comprising vapour 10 is work expanded in turbo-expander 12 to give a two phase stream 14 which is fed to the upper portion of a fractionation column in the form of demethaniser 16. A first liquid stream comprising liquid 18 is cooled in heat exchange system 20 to give sub-cooled liquid 22 which is expanded across valve 24 to give a stream 26 which may be liquid or two phase. Stream 26 is partially evaporated in heat exchange system 20 to give a two phase stream 28 which is fed to a mid-stage of the demethaniser 16.

[0052] Refrigeration for feed gas cooling is supplemented by evaporating liquid refrigerant stream 86 in heat exchange system 4 giving refrigerant vapour stream 88. Use of refrigerant from such a mechanical refrigeration cycle is dependent on feed gas composition, required recovery levels and economic factors, and is not an essential feature of the invention.

[0053] The residual vapour from the demethaniser 16 is rewarmed and compressed in the following manner. Vapour 30 from demethaniser 16 is warmed in heat exchange system 20 giving gas 32 which is further warmed in heat exchange system 4 to give gas 34. Gas 34 from heat exchange system 4 is compressed in expander brake 36 giving gas 38 which is cooled in cooler 40 giving gas 42. Gas 42 is compressed in 1st stage compressor 44 giving gas 46 which is subsequently cooled in cooler 48 giving gas 50. Gas 52, which is a portion of gas 50 is removed from the compression train, leaving Gas 54. Gas 54 is compressed in 2nd stage compressor 78 to give gas 80 which is cooled in cooler 82 to give a residue gas product 84.

[0054] Reflux to the demethaniser is provided in the following manner. Gas 52 from the 1 st stage compressor 44 discharge is cooled in heat exchange system 4 giving gas 56 and is condensed and subcooled in heat exchange system 20 giving a subcooled liquid 58. Subcooled liquid 58 is expanded across valve 60 to the demethaniser pressure, giving a two phase stream 62 which is fed to the top of the demethaniser 16.

[0055] Demethaniser reboil is provided in the following manner. Liquid 64 is drawn from a tray part way up the demethaniser and thermosyphoned through heat exchange system 4 where it is partially vaporised to give a two phase stream 66 which is fed back to the demethaniser. Similarly, liquid 68 is drawn from a tray lower down the demethaniser than that from which liquid 64 is drawn, and is thermosyphoned through heat exchange system 4 where it is partially vaporised to give a two phase stream 70 which is fed back to the demethaniser. Additionally, liquid 72 is thermosyphoned from the bottom tray and is fed to heat exchange system 4 where it is partially vaporised to give a two phase stream 74 which is fed back to the demethaniser. A stabilised liquid product 76 is drawn from the bottom of the demethaniser.

[0056] Operation of the separation apparatus depicted in Figure 2 is further illustrated by the data in Table 1.

[0057] The above process may be varied in a number of ways. For example one or more turbo-expansion steps may be utilized, or one or more steps of partial condensation and phase separation may be employed.

[0058] Another alternative to the process described above is to use the turbo-expander 12 to drive other rotating equipment, rather than drive a compressor used to supplement the residual gas compressors 44 and 78.

[0059] A further process option is to provide or supplement the refrigeration requirement by warming or evaporating the liquid product 76 from the demethaniser, either at the demethaniser pressure or at an elevated or reduced pressure appropriate to downstream processing.

[0060] The required refrigeration may also be provided or supplemented by one or more components of a refrigerant fluid being compressed, condensed/subcooled and expanded to one or more pressures enabling evaporation at one or more temperature levels. One or more liquid streams and a first residual vapour stream may result from heat exchange of the feed gas with this mechanical refrigeration cycle.

[0061] Yet another possible process improvement is to combine heat exchange systems 4 and 20, or to change heat exchange system 4 into one or more heat exchanger operations. Feed gas 2 may be split to optimise and improve practicability of heat integration within the aforementioned heat exchanger operations, and subsequently recombined to give stream 6.

[0062] Also, integration of the feed gas cooling and the demethaniser of the process can be optimised by utilizing more than two or less than two side exchangers.

[0063] The first embodiment described above may be varied as shown in Figure 3. The first liquid stream comprising liquid 18 from the first separator is expanded to an intermediate pressure and the resultant two phase stream 92 is separated in a second vapour/liquid separator 94. The further liquid stream comprising liquid 98 is subcooled in heat exchanger system 20, expanded and partially evaporated in heat exchanger system 20. The further gaseous stream comprising vapour 96 is combined with the residual gas recycle stream 56 and passed to heat exchanger system 20.

[0064] A second variation to the first embodiment is shown in Figure 4. The two phases of stream 14, the expander exhaust, are separated in a second vapour/liquid separator 90. The further liquid stream comprising liquid 96 is fed to the demethaniser. The further gaseous stream comprising vapour 92 is partially condensed in heat exchange system 20 and subsequently fed at a point in the demethaniser above the liquid feed.

Embodiment 2

[0065] The second embodiment of the invention is described below in terms of a process for high ethane recovery. The description should be read in conjunction with the flow diagram in Figure 5.

[0066] A feed gas at an elevated pressure 2 is passed through heat exchange system 4 where it is cooled and partially condensed to give a two phase stream 6. The liquid phase 48 is separated from the uncondensed vapour phase 10 in vapour/liquid separator 8. The first gaseous stream comprising vapour 10 is work expanded in turbo-expander 12 to give a two phase stream 14 which is fed to a mid point of a reequilibration device in the form of high pressure wash column 16. A first liquid stream comprising liquid 48 is expanded to a medium pressure across valve 50 to give a two phase stream 52 which is fed to the bottom of the high pressure wash column 16.

[0067] Refrigeration forfeed gas cooling is supplemented by evaporating liquid refrigerant stream 108 in heat exchange system 4 giving refrigerant vapour stream 110. Use of refrigerant from such a mechanical refrigeration cycle is dependent on feed gas composition, required recovery levels and economic factors, and is not an essential feature of the invention.

[0068] A first output from the high pressure wash column comprising liquid 36 is subcooled in heat exchange system 20 to give subcooled liquid 38. Liquid 38 is expanded across valve 40 to give stream 42, which may be liquid or two phase. Stream 42 is partially evaporated in heat exchange system 20 to give a two phase stream 46 which is fed to a mid stage of the demethaniser 54.

[0069] A second output from the high pressure wash column comprising vapour 18 is partially condensed in heat exchanger system 20 to give a two phase stream 22. An additional liquid stream comprising liquid 26 is separated from an uncondensed additional gaseous stream comprising vapour 62 in vapour/liquid separator 24. The liquid 26 is split, with a portion 28 being fed to reflux the high pressure wash column 16. The remaining portion 30 is expanded across valve 32 to give a two phase stream 34 which is fed to an upper part of the demethaniser 54, in order to provide the necessary reflux.

[0070] The residual vapour from the demethaniser is rewarmed and compressed in the following manner. Vapour 56 from demethaniser is warmed in heat exchange system 20 giving gas 58 which is further warmed in heat exchange system 4 to give gas 60. Gas 60 from heat exchange system 4 is compressed in the expander brake 68 giving gas 70 which is subsequently cooled in cooler 72 giving gas 74. Gas 74 is compressed in 1st stage compressor 76 to give gas 78 which is cooled in cooler 80 to give gas 82. Gas 82 is mixed with gas 66 to give gas 84. Gas 84 is compressed
in 2nd stage compressor 100 to give gas 102 which is cooled in cooler 104 to give a residue gas product 106.

[0071] The additional gaseous stream from the vapour/liquid separator 24 comprising residual vapour 62 is warmed in heat exchange system 20 giving gas 64 which is further warmed in heat exchange system 4 to give gas 66. Gas 66 from heat exchange system 4 is mixed with gas 82 to give gas 84.

[0072] Demethaniser reboil is provided in the following manner. Liquid 86 is drawn from a tray part way up the demethaniser and thermosyphoned through heat exchange system 4 where it is partially vaporised to give a two phase stream 88 which is fed back to the demethaniser. Similarly, Liquid 90 is drawn from a tray lower down the demethaniser than that from which liquid 86 is drawn, and is thermosyphoned through heat exchange system 4 where it is partially vaporised to give a two phase stream 92 which is fed back to the demethaniser. Additionally, liquid 94 is thermosyphoned from the bottom tray and is fed to heat exchange system 4 where it is partially vaporised to give a two phase stream 96 which is fed back to the demethaniser. A stabilised liquid product 98 is drawn from the bottom of the demethaniser.

[0073] Operation of the separation apparatus depicted in Figure 5 is further illustrated by the data in Table 2.

[0074] The above process may be varied in a number of ways. For example, one or more turbo-expansion steps may be utilized, or one or more steps of partial condensation and phase separation may be employed.

[0075] Another alternative to the process described above is to use the turbo-expander 12 to drive other rotating equipment, rather than drive a compressor used to supplement the residual gas compressors 76 and 100.

[0076] A further alternative is for one or both of (a) the portion of the additional liquid stream comprising liquid 26 which is fed to reflux the high pressure wash column and (b) the portion of liquid 26 which is fed to an upper part of the demethaniser 54, may be subcooled in heat exchange system 20 prior to passing to either the high pressure wash column 16 or valve 32 respectively.

[0077] Yet another possible process improvement is to combine heat exchange systems 4 and 20, or to change heat exchange system 4 into one or more heat exchanger operations. Feed gas 2 may be split to optimise and improve practicability of heat integration within the aforementioned heat exchanger operations, and subsequently recombined to give stream 6.

[0078] A further process option is to provide or supplement the refrigeration requirement by warming or evaporating the liquid product 98 from the demethaniser, either at the demethaniser pressure or at an elevated or reduced pressure appropriate to downstream processing. Alternatively, the refrigeration requirement may be provided or supplemented by expanding the residual vapours from the high pressure wash column.

[0079] The required refrigeration may also be provided or supplemented by one or more components of a refrigerant fluid being compressed, condensed/subcooled and expanded to one or more pressures enabling evaporation at one or more temperature levels. One or more liquid streams and a first residual vapour stream may result from heat exchange of the feed gas with this mechanical refrigeration cycle.

[0080] Integration of the feed gas cooling and the demethaniser of the process can be further optimised by utilizing more than two or less than two side exchangers.

[0081] It may also be advantageous within the above process to reboil the high pressure wash column, for example in heat exchange with a portion of feed gas, to reduce the load on the demethaniser.

[0082] As a further improvement, reflux to the high pressure wash column may be provided by totally condensing a portion of the high pressure wash column second output, comprising overhead vapour 18, rather than partially condensing the whole of vapour 18.

[0083] Also, the vapour and liquid phases of the expander exhaust stream 14 may be separated in a vapour/liquid separator, with the liquid phase being fed to a mid-stage of the high pressure wash column. The vapour phase may be partially condensed in heat exchange system 20 with the resultant two phase stream being fed at a higher point in the high pressure wash column to provide all or part of the required reflux.

Claims

1. A process for the separation of a heavier hydrocarbon fraction from a gaseous feed comprising a mixture of hydrocarbons, which process comprises:

(a) cooling the gaseous feed to produce a partially condensed stream

(b) separating the partially condensed stream to form a first liquid stream and a first gaseous stream

(c) subcooling at least a portion of the first liquid stream

(d) expanding said subcooled stream

(e) passing at least a portion of the expanded stream from (d) as a liquid feed to a fractionation column

(f) producing a cooled stream by cooling a separated lights fraction of the feed

(g) recovering said heavier hydrocarbon fraction as a bottoms fraction from said column

characterised in that (i) at least a part of the subcooling required in subcooling step (c) is provided by transfer of heat to the expanded stream from (d), (ii) at least a portion of the cold required to cool the separated lights fraction to produce said cooled stream (f) is provided by transfer of heat to the expanded stream from (d), and (iii) at least a portion of said cooled stream (f) is introduced to an upper part of the column.

2. A process according to Claim 1 in which at least a part of the subcooling required in subcooling step (c) is provided by transfer of heat to overhead vapour from said fractionation column.

3. A process according to Claim 1 or Claim 2 wherein overhead vapour from the fractionation column is heated in heat exchange with the first liquid stream from step (b) prior to expansion.

4. A process according to Claim 3 wherein overhead vapour from the fractionation column and the expanded stream from step (d) are heated in heat exchange with the first liquid stream from step (b) prior to expansion in a single heat exchanger.

5. A process according to Claim 4 wherein net refrigeration available within the heat exchanger is used to cool said separated lights fraction in step (f).

6. A process according to Claim 5 wherein said separated lights fraction comprises a recycle stream derived from overheads from the fractionation column.

7. A process of any of Claims 1 to 5 wherein overhead vapour from the fractionation column is rewarmed, compressed and cooled to provide a recycle stream and a residue gas product.

8. A process according to Claim 7 wherein overhead vapour from the fractionation column and the expanded stream from step (d) are heated in heat exchange with the subcooled first liquid stream from step (b) prior to expansion in a single heat exchanger.

9. A process according to Claim 8 wherein net refrigeration available within the heat exchanger is used to cool said separated lights fraction in step (f).

10. A process according to Claim 9 wherein said separated lights fraction comprises a recycle stream derived from overheads from the fractionation column.

11. A process according to Claim 10 wherein at least a portion of said recycle stream is condensed/subcooled and returned to an upper part of the fractionation column.

12. A process according to any preceding claim wherein said first liquid stream is expanded and separated to give a further gaseous stream and at least a portion of the remainder is subjected to the processes of steps (c) and (d).

13. A process according to Claim 12 wherein at least a part of said further gaseous stream is cooled to form at least a portion of cooled stream (f).

14. A process according to Claim 13 wherein said further gaseous stream or a portion thereof is combined with a recycled stream derived from column overheads to form said separated lights fraction, which is introduced into the fractionation column at a point above the liquid feed.

15. A process according to Claim 13 or 14 wherein said cooled stream (f) or a portion thereof is expanded prior to its introduction into the fractionation column.

16. A process according to any of Claims 13 to 15 wherein said further gaseous stream or a portion thereof is combined with the whole of said recycle stream prior to being transferred to the fractionation column.

17. A process according to any preceding claim wherein said cooled stream (f) or a portion thereof is expanded to produce an at least partially condensed stream which is introduced into the fractionation column.

18. A process according to Claim 17 wherein said first gaseous stream or a portion thereof is introduced into the fractionation column at a point above the liquid feed.

19. A process according to any of Claims 1 to 11 wherein said first gaseous stream is work expanded and separated to give a further gaseous stream and a further liquid stream, said further gaseous stream is partially condensed in a heat exchanger and then fed to the fractionation column.

20. A process according to Claim 19 wherein said further gaseous stream is introduced into the fractionation column at a point above the liquid feed.

21. A process according to Claim 19 or Claim 20 wherein said further liquid stream is also introduced into the fractionation column.

22. A process according to any of Claims 19 to 21 wherein said further gaseous stream is partially condensed in heat exchange with said expanded stream from step (d).

23. A process according to Claim 22 wherein overhead vapour from the fractionation column and the expanded stream from step (d) are heated in heat exchange with said first liquid stream from step (b) prior to expansion.

24. A process according to any of Claims 1 to 23 wherein one of said first gaseous stream and said first liquid stream is expanded and separated to give a further gaseous stream and a further liquid stream.

25. A process according to any of Claims 1 to 23 wherein both of said first gaseous stream and said first liquid stream are expanded, combined and separated to give a further gaseous stream and a further liquid stream.

26. A process according to any of Claims 12 to 24 wherein said first gaseous stream is work expanded prior to separation.

27. A process according to any of Claims 1 to 5 wherein said first gaseous stream and said first liquid stream are fed to a reequilibration device which produces a first output which is richer in heavier hydrocarbons than the first liquid stream, and a second output which is leaner in heavier hydrocarbons than the first gaseous stream, wherein said second output is cooled and partially condensed and directly or indirectly fed to an upper part of the fractionation column as said cooled stream (f) and wherein said first output is subjected the processes of steps (c) and (d).

28. A process according to Claim 27 wherein said first gaseous stream is work expanded before being fed to the reequilibration device.

29. A process according to Claim 27 or Claim 28 wherein said reequilibration device is a high pressure wash column.

30. A process according to any of Claims 27 to 29 wherein said second output is partially condensed in heat exchange with said expanded stream from step (d).

31. A process according to Claim 30 wherein said second output is partially condensed and at least a portion of the first liquid stream from step (b) is subcooled in heat exchange with said overhead vapour from said fractionation column and said expanded and at least partially evaporated subcooled stream from step (d).

32. A process according to Claim 30 or Claim 31 wherein said partially condensed output is fed to a separator, which produces an additional gaseous stream and an additional liquid stream, wherein at least a portion of said additional liquid stream is fed to an upper part of the fractionation column.

33. A process according to Claim 32 wherein at least a portion of said additional liquid stream is fed to the reequilibration device.

34. A process according to Claim 32 wherein said additional gaseous stream is warmed to produce a residual gas product.

35. A process according to any of Claims 32 to 34 wherein said additional gaseous stream is warmed in heat exchange with at least a portion of said first liquid stream from step (b) prior to expansion.

36. A process according to Claim 35 wherein said additional gaseous stream and said overhead vapour from said fractionation column are warmed in heat exchange with at least a portion of said first liquid stream from step (b) prior to expansion, and the second output from the reequilibration device.

37. A process according to any of Claims 27 to 36 wherein at least a portion of said first output is subcooled, expanded and at least partially evaporated, and at least a portion of the expanded and at least partially evaporated subcooled stream is used as a liquid feed for the fractionation column.

38. A process according to any of Claims 1 to 37 wherein an overhead fraction from said fractionation column is warmed, and successively compressed and cooled to produce a residue gas product.

39. A process according to Claim 38 wherein a portion of said residue gas product is cooled and recycled to the top of the fractionation column as said cooled stream (f).

40. Apparatus for the separation of a heavier hydrocarbon fraction from a gaseous feed comprising a mixture of hydrocarbons, wherein said mixture is cooled, partially condensed, separated into a first liquid stream and a first gaseous stream and at least a portion of each of the first liquid stream and the first gaseous stream are passed to a fractionation column in which said separation is carried out, which apparatus comprises:

(i) conduit means for transferring at least a portion of the first liquid stream to a heat exchanger in which said portion is subcooled,

(ii) means for expanding said subcooled stream,

(iii) conduit means for transferring at least a portion of said expanded stream to the heat exchanger in which the subcooling is effected, whereby at least a part of the subcooling is provided by transfer of heat to the expanded stream.

(iv) conduit means for introducing a cooled stream produced by cooling a separated lights fraction of the feed to an upper part of the column, at least a portion of the cold required to cool the separated lights fraction being provided by transfer of heat to said expanded stream

41. Apparatus according to Claim 40 wherein said cooled, partially condensed mixture is separated into a first gaseous stream and a first liquid stream in a first separator, and said apparatus further comprises means for expanding said first liquid stream and means for separating said first expanded liquid stream into a further gaseous stream and a further liquid stream, wherein said further liquid stream is transferred to the heat exchanger.

42. Apparatus according to Claim 40 further comprising means for partially condensing the first gaseous stream, separation means for separating at least a portion of said partially condensed stream into a further gaseous stream and a further liquid stream, and means for transferring at least a portion said further gaseous stream to the fractionation column.

43. Apparatus according to Claim 40 wherein said cooled, partially condensed mixture is separated into a first gaseous stream and a first liquid stream in a first separator, and said apparatus includes

(a) means for work expanding said first gaseous stream,

(b) means for expanding said first liquid stream,

(c) a reequilibration device which is arranged to receive said expanded first gaseous stream and said expanded first liquid stream, and produces a first output which is richer in heavier hydrocarbons than said first expanded liquid stream, and a second output which is leaner in heavier hydrocarbons than said first gaseous stream,

(d) conduit means for transferring at least a portion of said second output to the fractionation column, and

(e) conduit means for transferring said first output to the heat exchanger.

Ansprüche

1. Verfahren zur Abtrennung einer schwereren Kohlenwasserstoff-Fraktion aus einer gasförmigen Zufuhr, enthaltend ein Gemisch von Kohlenwasserstoffen, wobei das Verfahren umfasst:

(a) Abkühlen der gasförmigen Zufuhr, um einen teilweise kondensierten Strom zu produzieren

(b) Abtrennen des teilweise kondensierten Stroms, um einen ersten flüssigen Strom und einen ersten gasförmigen Strom zu bilden

(c) Unterkühlen mindestens eines Anteils des ersten flüssigen Stroms

(d) Expandieren des unterkühlten Stroms

(e) Führen mindestens eines Anteils des expandierten Stroms aus (d) als eine flüssige Zufuhr zu einer Fraktionierungskolonne

(f) Produzieren eines gekühlten Stroms durch Kühlen einer abgetrennten leichten Fraktion der Zufuhr

(g) Wiedergewinnen der schwereren Kohlenwasserstoff-Fraktion als eine Rückstandsfraktion aus der Kolonne
   dadurch gekennzeichnet, daß

(i) mindestens ein Teil des Unterkühlens, erforderlich im Unterkühlungsschritt (c), durch Wärmetransfer zum expandierten Strom aus (d) bereitgestellt wird,

(ii) mindestens ein Teil der Kälte, erforderlich, um die abgetrennten leichten Fraktionen zu kühlen, wodurch der gekühlte Strom (f) produziert wird, durch Wärmetransfer zum expandierten Strom aus (d) bereitgestellt wird und (iii) mindestens ein Anteil des gekühlten Stroms (f) an einem oberen Teil der Kolonne eingeleitet wird.

2. Verfahren nach Anspruch 1, in welchem mindestens ein Teil des Unterkühlens, erforderlich im Unterkühlungsschritt (c) durch Wärmetransfer zum Kopfprodukt-Dampf aus der Fraktionierungskolonne bereitgestellt wird.

3. Verfahren nach Anspruch 1 oder 2, wobei der Kopfprodukt-Dampf aus der Fraktionierungskolonne vor der Expansion im Wärmeaustausch mit dem ersten flüssigen Strom aus Schritt (b) erhitzt wird.

4. Verfahren nach Anspruch 3, wobei der Kopfprodukt-Dampf aus der Fraktionierungskolonne und der expandierte Strom aus Schritt (d) im Wärmeaustausch mit dem ersten flüssigen Strom aus Schritt (b) vor der Expansion in einem einzelnen Wärmeaustauscher erhitzt werden.

5. Verfahren nach Anspruch 4, wobei die Nettokälteerzeugung, verfügbar innerhalb des Wärmeaustauschers, verwendet wird, um die abgetrennte leichte Fraktion in Schritt (f) abzukühlen.

6. Verfahren nach Anspruch 5, wobei die abgetrennte Fraktion einen "Recycle"-Strom, der aus den Kopfprodukten aus der Fraktionierungskolonne stammt, umfaßt.

7. Verfahren nach einem der Ansprüche 1 bis 5, wobei der Kopfprodukt-Dampf aus der Fraktionierungskolonne wiedererwärmt, komprimiert und gekühlt wird, um einen "Recycle"-Strom und ein Restgasprodukt bereitzustellen.

8. Verfahren nach Anspruch 7, wobei der Kopfprodukt-Dampf aus der Fraktionierungskolonne und der expandierte Strom aus Schritt (d) im Wärmeaustausch mit dem unterkühlten ersten flüssigen Strom aus Schritt (b) vor der Expansion in einem einzelnen Wärmeaustauscher erhitzt werden.

9. Verfahren nach Anspruch 8, wobei die Nettokälteerzeugung, verfügbar innerhalb des Wärmeaustauschers, verwendet wird, um die abgetrennte leichte Fraktion in Schritt (f) abzukühlen.

10. Verfahren nach Anspruch 9, wobei die abgetrennte leichte Fraktion einen "Recycle"-Strom, der aus den Kopfprodukten aus der Fraktionierungskolonne stammt, umfaßt.

11. Verfahren nach Anspruch 10, wobei mindestens ein Anteil des "Recycle"-Stroms kondensiert/unterkühlt wird und zu einem oberen Teil der Fraktionierungskolonne zurückgeführt wird.

12. Verfahren nach irgendeinem vorgenannten Anspruch, wobei der erste flüssige Strom expandiert und abgetrennt wird, um einen weiteren gasfömnigen Strom zu ergeben und mindestens ein Anteil des Rückstands den Verfahren der Schritte (c) und (d) unterzogen wird.

13. Verfahren nach Anspruch 12, wobei mindestens ein Teil des weiteren gasförmigen Stroms gekühlt wird, um mindestens einen Anteil des gekühlten Stroms (f) zu bilden.

14. Verfahren nach Anspruch 13, wobei der weitere gasförmige Strom oder ein Anteil davon mit einem rezyklisierten Strom, der aus den Kolonnenkopfprodukten stammt, vereinigt wird, um die abgetrennte leichte Fraktion zu bilden, welche in die Fraktionierungskolonne an einem Punkt oberhalb der Flüssigkeitszufuhr eingeführt wird.

15. Verfahren nach Anspruch 13 oder 14, wobei der gekühlte Strom (f) oder ein Anteil davon vor seiner Einführung in die Fraktionierungssäule expandiert wird.

16. Verfahren nach einem der Ansprüche 13 bis 15, wobei der weitere gasförmige Strom oder ein Anteil davon mit der Gesamtheit des "Rerycle"-Stroms, bevor er zur Fraktionierungssäule überführt wird, vereinigt wird.

17. Verfahren nach irgendeinem vorhergehenden Anspruch, wobei der gekühlte Strom (f) oder ein Anteil davon expandiert wird, um mindestens einen teilweise kondensierten Strom zu erzeugen, welcher in die Fraktionierungssäule eingeführt wird.

18. Verfahren nach Anspruch 17, wobei der erste gasförmige Strom oder ein Anteil davon in die Fraktionierungskolonne an einem Punkt oberhalb der Flüssigkeitszufuhr eingeführt wird.

19. Verfahren nach einem der Ansprüche 1 bis 11, wobei der erste gasförmige Strom arbeitsexpandiert und abgetrennt wird, um einen weiteren gasförmigen Strom und einen weiteren flüssigen Strom zu ergeben, wobei der weitere gasförmige Strom teilweise in einem Wärmeaustauscher kondensiert wird und dann zur Fraktionierungskolonne zugeführt wird.

20. Verfahren nach Anspruch 19, wobei der weitere gasförmige Strom in die Fraktionierungskolonne an einem Punkt oberhalb der Flüssigkeitszufuhr eingeführt wird.

21. Verfahren nach Anspruch 19 oder 20, wobei der weitere flüssige Strom ebenfalls in die Fraktionierungskolonne eingeführt wird.

22. Verfahren nach einem der Ansprüche 19 bis 21, wobei der weitere gasförmige Strom im Wärmeaustausch mit dem expandierten Strom aus Schritt (d) teilweise kondensiert wird.

23. Verfahren nach Anspruch 22, wobei der Kopfprodukt-Dampf aus der Fraktionierungskolonne und der expandierte Strom aus Schritt (d) im Wärmeaustausch mit dem ersten flüssigen Strom aus Schritt (b) vor der Expansion erwärmt werden.

24. Verfahren nach einem der Ansprüche 1 bis 23, wobei entweder der erste gasförmige Strom oder der erste flüssige Strom expandiert und abgetrennt wird, um einen weiteren gasförmigen Strom und einen weiteren flüssigen Strom zu ergeben.

25. Verfahren nach einem der Ansprüche 1 bis 23, wobei sowohl der erste gasförmige Strom als auch der erste flüssige Strom expandiert, vereinigt und abgetrennt wird, um einen weiteren gasförmigen Strom und einen weiteren flüssigen Strom zu ergeben.

26. Verfahren nach einem der Ansprüche 12 bis 24, wobei der erste gasförmige Strom vor der Abtrennung arbeitsexpandiert wird.

27. Verfahren nach einem der Ansprüche 1 bis 5, wobei der erste gasförmige Strom und der erste flüssige Strom einem Reäquilibrierungsgerät zugeführt werden, welches einen ersten "Output", welcher an schwereren Kohlenwasserstoffen reicher als der erste flüssige Strom ist, und einen zweiten "Output" produziert, welcher an schwereren Kohlenwasserstoffen ärmer als der erste gasförmige Strom ist, wobei der zweite "Output" gekühlt und teilweise kondensiert wird und direkt oder indirekt einem oberen Teil der Fraktionierungskolonne als gekühlter Strom (f) zugeführt wird und wobei der erste "Output" den Verfahren der Schritte (c) und (d) unterzogen wird.

28. Verfahren nach Anspruch 27, wobei der erste gasförmige Strom, bevor er dem Reäquilibrierungsgerät zugeführt wird, arbeitsexpandiert wird.

29. Verfahren nach Anspruch 27 oder 28, wobei das Reäquilibrierungsgerät eine Hochdruckwaschkolonne ist.

30. Verfahren nach einem der Ansprüche 27 bis 29, wobei der zweite "Output" im Wärmeaustausch mit dem expandierten Strom aus Schritt (d) teilweise kondensiert wird.

31. Verfahren nach Anspruch 30, wobei der zweite "Output" teilweise kondensiert wird und mindestens ein Anteil des ersten flüssigen Stroms aus Schritt (b) im Wärmeaustausch mit dem Kopfprodukt-Dampf aus der Fraktionierungskolonne und dem expandierten und zumindest teilweise verdampften, unterkühlten Strom aus Schritt (d) unterkühlt wird.

32. Verfahren nach Anspruch 30 oder 31, wobei der teilweise kondensierte "Output" einem Separator zugeführt wird, welcher einen zusätzlichen gasförmigen Strom und einen zusätzlichen flüssigen Strom produziert, wobei mindestens ein Anteil des zusätzlichen flüssigen Stroms einem oberen Teil der Fraktionierungskolonne zugeführt wird.

33. Verfahren nach Anspruch 32, wobei mindestens ein Anteil des zusätzlichen flüssigen Stroms dem Reäquilibrierungsgerät zugeführt wird.

34. Verfahren nach Anspruch 32, wobei der zusätzliche gasförmige Strom erwärmt wird, um ein Restgasprodukt zu produzieren.

35. Verfahren nach einem der Ansprüche 32 bis 34, wobei der zusätzliche gasförmige Strom im Wärmeaustausch mit mindestens einem Anteil des ersten flüssigen Stroms aus Schritt (b) vor der Expansion erwärmt wird.

36. Verfahren nach Anspruch 35, wobei der zusätzliche gasförmige Strom und der Kopfprodukt-Dampf aus der Fraktionierungskolonne im Wärmeaustausch mit mindestens einem Anteil des ersten flüssigen Stroms aus Schritt (b) vor der Expansion und dem zweiten "Output" aus dem Reäquilibrierungsgerät erwärmt werden.

37. Verfahren nach einem der Ansprüche 27 bis 36, wobei mindestens ein Anteil des ersten "Outputs" unterkühlt, expandiert und mindestens teilweise verdampft wird und mindestens ein Anteil des expandierten und zumindest teilweise verdampften unterkühlten Stroms als eine flüssige Zufuhr für die Fraktionierungskolonne verwendet wird.

38. Verfahren nach einem der Ansprüche 1 bis 37, wobei eine Kopfprodukt-Fraktion aus der Fraktionierungskolonne erwärmt und sukzessiv komprimiert und abgekühlt wird, um ein Restgasprodukt zu produzieren.

39. Verfahren nach Anspruch 38, wobei ein Anteil des Restgasprodukts gekühlt und zur Spitze der Fraktionierungskolonne als gekühlter Strom (f) rückgeführt wird.

40. Vorrichtung zur Abtrennung einer schwereren Kohlenwasserstoff-Fraktion aus einer gasförmigen Zufuhr, umfassend ein Gemisch von Kohlenwasserstoffen, wobei das Gemisch gekühlt, teilweise kondensiert und in einen ersten flüssigen Strom und einen ersten gasförmigen Strom separiert wird und mindestens ein Anteil von sowohl dem ersten flüssigen Strom als auch dem ersten gasförmigen Strom zu einer Fraktionierungskolonne geführt wird, in welcher die Separierung vorgenommen wird, wobei die Vorrichtung umfaßt

(i) Leitungsmittel zum Überführen mindestens eines Anteils des ersten flüssigen Stroms zu einem Wärmeaustauscher, in welchem dieser Anteil unterkühlt wird,

(ii) Mittel zum Expandieren des unterkühlten Stroms,

(iii) Leitungsmittel zum Überführen mindestens eines Anteils des expandierten Stroms zu einem Wärmeaustauscher, in welchem das Unterkühlen bewirkt wird, wobei mindestens ein Teil des Unterkühlens durch Wärmetransfer zum expandierten Strom zur Verfügung gestellt wird,

(iv) Leitungsmittel für das Einführen eines gekühlten Stroms, produziert durch Kühlen einer abgetrennten leichten Fraktion der Zufuhr zu einem oberen Teil der Kolonne, wobei mindestens ein Anteil der Kälte, die erforderlich ist, um die abgetrennte leichte Fraktion zu kühlen, durch Wärmetransfer zu dem expandierten Strom bereitgestellt wird.

41. Vorrichtung nach Anspruch 40, wobei das gekühlte, teilweise kondensierte Gemisch in einem ersten Separator in einen ersten gasförmigen Strom und in einen ersten flüssigen Strom aufgeteilt wird und die Vorrichtung weiterhin Mittel zum Expandieren des ersten flüssigen Stroms und Mittel zur Auftrennung des ersten expandierten flüssigen Stroms in einen weiteren gasförmigen Strom und einen weiteren flüssigen Strom umfaßt, wobei der weitere flüssige Strom zum Wärmeaustauscher überführt wird.

42. Vorrichtung nach Anspruch 40, weiter umfassend Mittel zum teilweisen Kondensieren des ersten gasförmigen Stroms, Separierungsmittel zum Auftrennen mindestens eines Anteils des teilweise kondensierten Stroms in einen weiteren gasförmigen Strom und einen weiteren flüssigen Strom und Mittel zum Überführen mindestens eines Anteils des weiteren gasförmigen Stroms zur Fraktionierungskolonne.

43. Vorrichtung nach Anspruch 40, wobei das gekühlte, teilweise kondensierte Gemisch in einem ersten Separator in einen ersten gasförmigen Strom und einen ersten flüssigen Strom aufgetrennt wird und die Vorrichtung einschließt

(a) Mittel zum Arbeitsexpandieren des ersten gasförmigen Stroms,

(b) Mittel zum Expandieren des ersten flüssigen Stroms,

(c) ein Reäquilibrierungsgerät, welches angeordnet ist, um den expandierten ersten gasförmigen Strom und den expandierten ersten flüssigen Strom aufzunehmen und welches einen ersten "Output", welcher an schwereren Kohlenwasserstoffen reicher als der erste expandierte flüssige Strom ist, und einen zweiten "Output" produziert, welcher an schwereren Kohlenwasserstoffen ärmer als der erste gasförmige Strom ist,

(d) Leitungsmittel zum Überführen mindestens eines Anteils des zweiten "Outputs" zur Fraktionierungskolonne und

(e) Leitungsmittel zum Überführen des ersten "Outputs" zum Wärmeaustauscher.

Revendications

1. Procédé pour la séparation d'une fraction d'hydrocarbure lourde dans une arrivée de gaz comprenant un mélange d'hydrocarbures, ce procédé comprenant les étapes consistant à :

(a) refroidir l'arrivée de gaz pour produire un flux partiellement condensé

(b) séparer le flux partiellement condensé pour former un premier flux liquide et un premier flux gazeux

(c) sous-refroidir au moins une portion du premier flux liquide

(d) dilater ledit flux sous-refroidi

(e) faire passer au moins une portion du flux dilaté issu de (d) sous forme d'arrivée liquide dans une colonne de fractionnement

(f) produire un flux refroidi en refroidissant une fraction légère séparée de l'arrivée

(g) récupérer la fraction d'hydrocarbures plus lourde comme fraction inférieure de ladite colonne.
   caractérisé en ce que (i) au moins une partie du sous-refroidissement requis à l'étape de sous-refroidissement (c) est assurée par le transfert de chaleur vers le flux dilaté issu de (d), (ii) au moins une partie du froid requis pour refroidir la fraction légère séparée pour produire ledit flux refroidi (f) est assurée par le transfert de chaleur vers le flux dilaté issu de (d), et (iii) au moins une portion dudit flux refroidi (f) est introduite dans une partie supérieure de la colonne.

2. Procédé selon la revendication 1 dans lequel au moins une partie du sous-refroidissement requis à l'étape de sous-refroidissement (c) est assurée par le transfert de chaleur en vapeur de tête depuis ladite colonne de fractionnement.

3. Procédé selon la revendication 1 ou la revendication 2, dans lequel la vapeur de tête de la colonne de fractionnement est chauffée dans un échangeur thermique avec le premier flux liquide issu de l' étape (b) avant dilatation.

4. Procédé selon la revendication 3 dans lequel la vapeur de tête issue de la colonne de fractionnement et le flux dilaté issu de l'étape (d) sont chauffés dans un échangeur thermique avec le premier flux liquide issu de l'étape (b) avant dilatation dans un échangeur de chaleur simple.

5. Procédé selon la revendication 4 dans lequel la réfrigération nette disponible dans l'échangeur thermique est utilisée pour refroidir ladite fraction légère séparée à l'étape (f).

6. Procédé selon la revendication 5 dans lequel ladite fraction légère séparée comprend un flux de recyclage dérivé des fractions de tête issues de la colonne de fractionnement.

7. Procédé selon l'une des revendications 1 à 5 dans lequel la vapeur de tête issue de la colonne de fractionnement est réchauffée, comprimée et refroidie pour fournir un flux de recyclage et un produit de gaz résiduel.

8. Procédé selon la revendication 7 dans lequel la vapeur de tête issue de la colonne de fractionnement et le flux dilaté issu de l'étape (d) sont chauffés dans un échangeur de chaleur avec le premier flux liquide sous-refroidi issu de l'étape (b) avant sa dilatation dans un échangeur thermique simple.

9. Procédé selon la revendication 8 dans lequel la réfrigération nette disponible dans l'échangeur thermique est utilisée pour refroidir lesdites fractions légères séparées à l'étape (f).

10. Procédé selon la revendication 9 dans lequel ladite fraction légère séparée comprend un flux de recyclage dérivé des fractions de tête issues de la colonne de fractionnement.

11. Procédé selon la revendication 10 dans lequel au moins une portion dudit flux de recyclage est condensée/sous-refroidie et renvoyée vers une partie supérieure de la colonne de fractionnement.

12. Procédé selon l'une des revendications précédentes, dans lequel ledit flux liquide est dilaté et séparé pour produire un flux gazeux ultérieur et au moins une partie du reste est soumise aux processus des étapes (c) et (d).

13. Procédé selon la revendication 12 dans lequel au moins une partie dudit flux gazeux ultérieur est refroidie pour former au moins une portion du flux refroidi (f).

14. Procédé selon la revendication 13 dans lequel ledit flux gazeux ultérieur ou une portion dudit est combinée avec un flux recyclé dérivé des fractions de tête de la colonne pour former ladite fraction légère séparée, qui est introduite dans la colonne de fractionnement en un point situé au-dessus de l'arrivée de liquide.

15. Procédé selon la revendication 13 ou 14, dans lequel ledit flux refroidi (f) ou une portion dudit est dilaté avant son introduction dans la colonne de fractionnement.

16. Procédé selon l'une des revendications 13 à 15, dans lequel ledit flux gazeux ultérieur ou une portion dudit est combinée avec la totalité du flux de recyclage avant d'être transférée vers la colonne de fractionnement.

17. Procédé selon l'une des revendications précédentes, dans lequel ledit flux refroidi (f) ou une portion dudit est dilaté pour produire un flux au moins partiellement condensé qui est introduit dans la colonne de fractionnement.

18. Procédé selon la revendication 17 dans lequel ledit flux gazeux ou une portion dudit est introduit dans la colonne de fractionnement en un point situé au-dessus de l'arrivée de liquide.

19. Procédé selon l'une des revendications 1 à 11 dans lequel le premier flux gazeux est dilaté par travail et séparé pour donner un flux gazeux conséquent et un flux liquide conséquent, ledit flux gazeux conséquent étant partiellement condensé en un échangeur de chaleur puis envoyé vers la colonne de fractionnement.

20. Procédé selon la revendication 19 dans lequel ledit flux gazeux ultérieur est introduit dans la colonne de fractionnement en un point situé au-dessus de l'arrivée de liquide.

21. Procédé selon la revendication 19 ou la revendication 20, dans lequel ledit flux liquide est également introduit dans la colonne de fractionnement.

22. Procédé selon l'une des revendications 19 à 21 dans lequel ledit flux gazeux est partiellement condensé dans un échangeur thermique avec ledit flux dilaté issu de l'étape (d).

23. Procédé selon la revendication 22 dans lequel la vapeur de tête issue de la colonne de fractionnement et le flux dilaté issu de l'étape (d) sont chauffés dans un échangeur thermique avec ledit flux liquide issu de l'étape (b) avant dilatation.

24. Procédé selon l'une des revendications 1 à 23 dans lequel l'un des premier flux gazeux et premier flux de liquide est dilaté et séparé pour donner un flux gazeux conséquent et un flux liquide conséquent.

25. Procédé selon l'une des revendications 1 à 23 dans lequel ledit premier flux gazeux et ledit premier flux liquide sont dilatés, combinés et séparés pour donner un flux gazeux conséquent et un flux liquide conséquent.

26. Procédé selon l'une des revendications 12 à 24, dans lequel ledit flux gazeux est dilaté par travail avant séparation.

27. Procédé selon l'une des revendications 1 à 5 dans lequel ledit premier flux gazeux et ledit premier flux liquide sont envoyés dans un dispositif de rééquilibrage qui produit une première sortie qui est riche en hydrocarbures plus lourds que le premier flux liquide, et une seconde sortie qui est plus pauvre en hydrocarbures plus lourds que le premier flux gazeux, dans lequel la seconde sortie est refroidie et partiellement condensée et directement ou indirectement amenée vers une partie supérieure de la colonne de fractionnement sous forme de flux refroidi (f) et dans lequel ladite première sortie est soumise aux processus des étapes (c) et (d).

28. Procédé selon la revendication 27 dans lequel le premier flux gazeux est dilaté par travail avant d'être envoyé vers le dispositif de rééquilibrage.

29. Procédé selon la revendication 27 ou la revendication 28, dans lequel ledit dispositif de rééquilibrage est une colonne de lavage haute pression.

30. Procédé selon l'une des revendications 27 à 29, dans lequel ladite seconde sortie est partiellement condensée dans un échangeur thermique avec ledit flux dilaté issu de l'étape (d).

31. Procédé selon la revendication 30 dans lequel ladite seconde sortie est partiellement condensée et au moins une portion du premier flux liquide issu de l'étape (b) est sous-refroidie dans l'échangeur thermique avec ladite vapeur de tête issue de ladite colonne de fractionnement et ledit flux sous-refroidi dilaté et au moins partiellement évaporé issu de l'étape (d).

32. Procédé selon la revendication 30 ou la revendication 31, dans lequel ladite sortie partiellement condensée est envoyée vers un séparateur, qui produit un flux gazeux supplémentaire et un flux liquide supplémentaire, dans lequel au moins une portion du flux liquide supplémentaire est envoyée vers une partie supérieure de la colonne de fractionnement.

33. Procédé selon la revendication 32, dans lequel au moins une partie dudit flux liquide supplémentaire est envoyée vers le dispositif de rééquilibrage.

34. Procédé selon la revendication 32, dans lequel ledit flux gazeux supplémentaire est chauffé pour produire un produit gazeux résiduel.

35. Procédé selon l'une des revendications 32 à 34 dans lequel ledit flux gazeux additionnel est chauffé dans un échangeur thermique avec au moins une portion dudit premier flux liquide issu de l'étape (b) avant dilatation.

36. Procédé selon la revendication 35, dans lequel ledit flux gazeux supplémentaire et ladite vapeur de tête issue de ladite colonne de fractionnement sont chauffés dans un échangeur thermique avec au moins une portion dudit premier flux liquide issu de l'étape (b) avant dilatation, et la seconde sortie est issue du dispositif de rééquilibrage.

37. Procédé selon l'une des revendications 27 à 36 dans lequel au moins une portion de ladite première sortie est sous-refroidie, dilatée et au moins partiellement évaporée, et au moins une partie du flux sous-refroidi dilaté et au moins partiellement évaporé est utilisé comme alimentation liquide pour la colonne de fractionnement.

38. Procédé selon l'une des revendications 1 à 37 dans lequel une fraction de tête de la dite colonne de fractionnement est réchauffée puis comprimée et refroidie pour produire un produit de gaz résiduel.

39. Procédé selon la revendication 38 dans lequel une portion dudit gaz produit résiduel est refroidie et recyclée dans le haut de la colonne de fractionnement pour produire ledit flux refroidi (f).

40. Dispositif pour la séparation d'une fraction d'hydrocarbure plus lourde dans une arrivée de gaz comprenant un mélange d'hydrocarbures, dans lequel ledit mélange est refroidi, partiellement condensé, séparé en un premier flux liquide et un premier flux gazeux et au moins une partie du premier flux liquide et une partie du premier flux gazeux sont envoyées dans une colonne de fractionnement dans laquelle ladite séparation est effectuée, lequel dispositif comprend :

(i) un moyen de conduit pour transférer au moins une partie du premier flux liquide vers un échangeur thermique dans lequel ladite portion est sous-refroidie,

(ii) des moyens pour dilater ledit flux sous-refroidi,

(iii) un moyen de conduit pour transférer au moins une partie dudit flux dilaté vers l'échangeur thermique dans lequel le sous-refroidissement est effectué, ce par quoi au moins une partie du sous-refroidissement est assuré par le transfert de chaleur vers le flux dilaté.

(iv) un moyen de conduit pour introduire un flux refroidi produit en refroidissant une fraction légère séparée de l'alimentation vers une partie supérieure de la colonne, au moins une portion du froid requis pour refroidir la fraction légère séparée étant fournie par le transfert de chaleur vers ledit flux dilaté.

41. Dispositif selon la revendication 40 dans lequel le mélange refroidi, partiellement condensé est séparé en un premier flux gazeux et un premier flux liquide dans un premier séparateur, et ledit dispositif comprend en outre des moyens pour dilater ledit flux liquide et des moyens pour séparer ledit premier flux liquide dilaté en un flux gazeux conséquent et un flux liquide conséquent, dans lequel ledit flux liquide conséquent est transféré vers l'échangeur thermique.

42. Dispositif selon la revendication 40, comprenant en outre des moyens pour condenser partiellement le premier flux gazeux, des moyens de séparation pour séparer au moins une portion dudit flux partiellement condensé en un flux gazeux conséquent et un flux liquide conséquent, et des moyens pour transférer au moins une portion dudit flux gazeux vers la colonne de fractionnement.

43. Dispositif selon la revendication 40 dans lequel ledit mélange refroidi, partiellement condensé est séparé en un premier flux gazeux et un premier flux liquide dans un premier séparateur, et ledit dispositif inclut :

(a) des moyens pour dilater par travail ledit premier flux gazeux,

(b) des moyens pour dilater ledit premier flux liquide,

(c) un dispositif de rééquilibrage qui est disposé pour recevoir ledit premier flux gazeux dilaté et ledit premier flux liquide dilaté, et produit une première sortie qui est plus riche en hydrocarbures plus lourds que ledit premier flux liquide dilaté, et une seconde sortie qui est plus lourde en hydrocarbures plus lourds que ledit premier flux gazeux,

(d) des moyens de conduit pour transférer au moins une portion de ladite sortie vers la colonne de fractionnement, et

(e) des moyens de conduit pour transférer ladite première sortie vers l'échangeur thermique.

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